Question

Immunity’s Early-Warning System. Scientific American, January 2005.

How does the innate immune system recognize pathogens?

After recognizing pathogens, what is the response of the innate immune system? (ie. What action does it take?)

How does the innate immune response promote and adaptive immune response?

How can an immune response contribute to disease?

How can exposure to LPS lead to septic shock? What is a situation in which one would be exposed to LPS?

In what organism were Toll proteins first discovered?

What happens when a bacteria binds a TLR, for example LPS binding to TLR-4? How is the signal transmitted from the receptor to the cell, and in general what does it tell the cell to do?

Which TLR is a current target for improving the effectiveness of vaccines, ie. To act as an adjuvant?

Answer 1

1) The innate immune system or non-specific immune system is an important subsystem of the immune system . The innate immune system lacks the specificity of adaptive immunity, however, it can distinguish nonself from self. They depend on a group of proteins and phagocytic cells that recognize conserved features of pathogens and become quickly activated to help destroy invaders. Proteins that recognize features common to many pathogens occur as secreted molecules and as receptors on cells of the innate immune system. The receptors of the innate immune system are typically not clonally distributed; a given set of receptors will be present on all the cells of the same cell type. The binding of pathogens by these receptors gives rise to very rapid responses. At the time of infection, molecules that are broadly shared by pathogens but distinguishable from host molecules, collectively referred to as pathogen-associated molecular patterns (PAMPs) are recognised by immune cells such as macrophages, dendritic cells, histiocytes, Kupffer cells, and mastocytes which present receptors contained on the surface or within the cell, named pattern recognition receptors (PRRs). At the onset of an infection, burn, or other injuries, these cells undergo activation and bring about immune response.

2) After recognition of a non-self antigen, innate immune system mounts a general immune response such as inflammation, complement, and non-specific cellular responses. The inflammatory response actively brings immune cells to the site of an infection by increasing blood flow to the area. Complement is an immune response that marks pathogens for destruction and is responsible for degradation of cell membrane of the pathogen.

3) Antigen presenting cells (APCs) of the innate immune system display the epitope of the antigens they have engulfed by means of  major histocompatibility complex (MHC) molecules on its surface. This alerts the adaptive immune system and allows cells known as T cells to recognize an infected cell. Pattern-recognition receptors (PRRs) found on or inside phagocytes, recognize general groups of microbes that have common traits. They set in motion a sequence of cellular events that results in posting the flags required to trigger an adaptive immune response. They also release a family of chemical messengers called cytokines to call the adaptive immune system into action.